2 Samuel 5:1-4

Then all the tribes of Israel came to David at Hebron and said, “Behold, we are your bone and your flesh.

Previously, when Saul was king over us, you were the one who led Israel out and in. And the Lord said to you, ‘You will shepherd My people Israel, and you will be a leader over Israel.’ ”

So all the elders of Israel came to the king at Hebron, and King David made a covenant with them before the Lord in Hebron; then they anointed David king over Israel.

David was thirty years old when he became king, and he reigned for forty years.